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1.
《山地学报》2015,(6)
冰川终碛湖溃决引发的大规模山洪泥石流灾害,常给下游沿河一带造成重大人员伤亡和财产损失,受到社会广泛关注。冰川终碛湖一次溃决常未到底,其部分溃决后,残留湖因源头冰川进退、冰舌持续消融致后期湖面面积增大,湖水量增加,作者将这种现象定义为冰川终碛湖溃决-再生现象。以西藏波密米堆沟光谢错和聂拉木章藏布次仁玛错冰湖为研究对象,基于前人研究成果,利用遥感解译方法,分析了光谢错和次仁玛错冰湖面积的变化和冰川末端进退变化的特征。研究表明:光谢错、次仁玛错呈现出冰湖面积增大→溃决缩小→面积再增大的过程,光谢错在1988年溃决后面积已恢复至溃决前的63.6%,次仁玛错在1981年溃决后面积已基本恢复至溃决前的大小;从1980年代末至现在,贡扎冰川、阿玛次仁冰川末端处于退缩状态,终碛湖面积呈扩张状态。结合波密、聂拉木两气象站多年年降水量和年平均气温观测资料进行同步对比分析,初步探讨了冰川终碛湖再生现象的机理:1.冰川末端的前进与后退是冰湖面积变化的主导者,冰舌前进推动湖盆底冰碛物和溃口两侧岸坡垮塌导致堵塞泄流通道,冰川末端的退缩提供了空间条件;2.持续高温与强降雨的耦合作用是冰湖溃决的直接激发条件,持续高温累积是冰川消融冰湖面积增大的主要因素。 相似文献
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为查明雷琼火山群中九斗洋干玛珥湖的第四纪地层空间展布,以及埋藏古火山形态,为后续研究提供地质背景资料,采用高效、便捷的高密度电阻率法对九斗洋干玛珥湖湖盆区进行勘测,并结合钻孔岩芯的研究进行验证。得出的主要结论为：1）盆地深部地层最高电阻率可达到300 Ω?m以上,盆地中央基岩以下存在高阻地质体,推测为岩浆通道位置。岩浆经过通道溢出后横向展布,覆于沉积地层上,随后在火山口内形成湖泊,堆积第四纪湖相沉积,其火山机构与玛珥湖型火山一致;2）九斗洋干玛珥湖第四纪松散沉积地层的电阻率通常＜60 Ω?m,泥炭层电阻率最低;3）第四纪沉积总厚度为25~50 m,盆地松散沉积的岩浆岩基底总体平整,但尚有波状起伏。研究结果表明,高密度电阻率法结合钻孔验证是研究火山机构形态及火山口湖第四纪沉积空间展布的有效方法。 相似文献
3.
藏南沉错地区近1400年来的介形类与环境变化 总被引：7，自引：0，他引：7
通过分析藏南沉错CC1孔的介形类动物群所提供的古环境信息，探讨近1400年来的湖泊演化。CC1孔介形类共计7属15种。据其属种，数量及生态特征，可划分为7个组合，同时发现1400年来沉错环境变化可分为3个时期：（1）公元6世末－14世纪下半叶沉错主要为较深水湖，其中大约在708－780年和1199－1213年湖泊迅速扩大加深；（2）14世纪下半叶－19世纪末沉错主要为浅水湖，其中大约在1454－1525年，1645－1670年和1803－1891年3个时段湖泊强烈退缩，环境极不稳定，而大约在1731－1803年湖泊发生逆向转化，湖水增多，湖面抬升；（3）19世纪末至今沉错由较深水湖转变为浅水湖，20世纪60年代以前为较深水湖，其中大约在1929－1935年湖泊急剧加深，20世纪70年代以来湖泊退缩，湖水变浅。 相似文献
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青藏高原可可西里地区玛章错钦湖畔苟纠麦尕沟的泥火山机理雏议 总被引：10，自引：1，他引：9
通过可可里西地区综合科学考察发现了玛章错钦湖畔苟纠麦尕沟的泥火山,本文对其泥火山机构进行了分类及其物质鉴定,恢复了其形成环境和喷发形式,并指出青藏高原腹地晚新生代盆地有赋存油气藏的可能。 相似文献
6.
利用电镜扫描的方法分析了南极阿德雷岛Y2湖企鹅粪土沉积层中石英砂微形貌的特征,发现在企鹅粪含量高的沉积层中石英砂表面具有明显的碗状溶蚀坑等化学溶蚀特征,这一溶蚀特征在Y2湖企鹅粪含量低的沉积层和研究区的其他未受企鹅粪影响的沉积环境中均未明显出现。为了揭示这一特殊化学溶蚀现象的作用机制,根据Y2湖企鹅粪土沉积层自然沉积环境,通过条件实验确定在实验室内使用酸性较高的氟溶液(1mol.L-1HF溶液)对石英砂进行溶蚀实验,通过对比分析发现,实验室模拟条件下可以得到与企鹅粪土沉积层中石英砂相近的表面微形貌特征,这表明它们是在相似的过程中形成的。企鹅粪土沉积层酸性高氟环境中可能存在的HF酸化学溶蚀作用是形成企鹅粪土层中石英砂表面特有溶蚀坑的主要原因。在南极特殊的自然条件下碗状溶蚀坑与企鹅粪之间存在一定的因果关系,从而使石英砂的表面微形貌分析成为南极企鹅生态研究的一种新的辅助手段。 相似文献
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巴松错又名错高湖,意为绿色的水,湖面3700多米。巴松错如镶嵌在高峡深谷中的一轮新月,长约12公里,湖宽几百至数千米不等。最深处66多米。总面积25.9平方公里。 相似文献
11.
M. Horrocks W. T. Baisden J. Flenley D. Feek L. González Nualart S. Haoa-Cardinali T. Edmunds Gorman 《Journal of Paleolimnology》2012,48(4):767-783
Previous paleoenvironmental records from the lake of Rano Raraku crater, Easter Island??s statue quarry, showed evidence of two major environmental changes, fluctuating lake levels and Polynesian forest clearance. There have been no reports, however, of former shorelines and it is not known if deforestation of the crater was for quarrying alone, or also for agriculture. We shed light on this by examining macrofossil casts of plants found in dryland iron pan deposits, and using combined analyses of pollen, phytoliths and starch in a lake sediment core and dryland soil profile. Casts of wetland taxa, namely Scirpus californicus and fern rhizomes, were identified in the iron pan deposits up to ~10?m above the current lake level, providing evidence of higher lake level during the last Glacial period. This height is near the level of the col on the western side of the crater, indicating that the lake was at its maximum possible elevation at the time, with overflow via the col. Microfossils of introduced Colocasia esculenta (taro), Ipomoea batatas (sweet potato), Musa (banana sp.) and possibly Lagenaria siceraria (bottle gourd) were identified in the core and soil profile, providing evidence of ancient Polynesian agriculture. Earliest evidence of gardening occurs at ~627?C513?cal BP, immediately after large-scale forest clearance. The core and soil profile were located on opposite sides of the catchment, suggesting that the crater was intensively multi-cropped and that widespread irrigated gardens co-existed with statue-quarrying activity. 相似文献
12.
The 12 km wide and about 175 m deep El’gygytgyn crater lake in Central Chukotka, NE Siberia, is of special interest for investigation
as it could provide the first undisturbed 3.6 Ma terrestrial record from the Arctic realm, reaching back a million years before
the first major glaciation of the Northern Hemisphere. A single-channel seismic survey was carried out on an expedition to
the lake in 2000, in which both high resolution and deep penetration data were acquired. Seismic data suggest an impact crater
structure in Cretaceous volcanic bedrock, indicated by velocities of >5000 m s−1, whose upper 500–600 m is brecciated. The lake is filled with two units of sediments, the upper one well stratified and the
lower one massive. In the center of the lake, the combined thickness of the two sedimentary units is estimated to be 320–350 m.
The upper unit is draped over the location of an interpreted central peak and is locally intercalated with debris flows, mainly
in the western part of the lake and at the lake margins. Most of the lower unit is obscured by multiples as a result of high
reflection coefficients in the upper unit. As at least the upper unit appears to be undisturbed by glaciation, the lake should
yields unique information on the paleoclimatic development of the East Siberian Arctic.
This is the fourth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
13.
A. Fepuleai S. J. Gale N. A. Wales S. P. L. McInerney K. K. Lal B. V. Alloway 《Journal of Paleolimnology》2018,60(4):473-493
The two largest islands of the Samoan chain, Savai’i and Upolu, possess almost 400 volcanic cones. Their craters form enclosed, internally drained basins that potentially retain long, detailed and uninterrupted sedimentary sequences. Because of the sparsity, fragmentary nature and low temporal resolution of records of environmental change from the tropical Pacific, these deposits have the potential to fill an important gap in our knowledge of global climatic and environmental change. To interpret such records we must understand the depositional processes that operate in these basins. Unfortunately, although the post-eruptive sedimentology of volcanic calderas and maars is relatively well-established, that of crater lakes remains poorly understood. The volcanic edifice of Mount Lanotō in southeast Upolu was selected for investigation. The form of the volcano and its crater are typical of those observed across the island. The sediments retained in the crater are composed largely of plant-organic-rich muds that display little visible evidence of stratigraphic variation. Mineral magnetic and chemical methods were therefore employed to document the types and distribution of sedimentary facies represented in the post-eruptive crater fill and, by inference, the processes of sedimentation that had operated in the crater. The earliest post-eruptive deposits are the result of the failure of the crater’s oversteepened internal slopes. The crater floor subsequently collapsed to form a pit crater. The basal deposits in the pit crater are likely to be the product of the collapse of its walls and roof. However, the bulk of the material in the feature was laid down under lacustrine conditions. These deposits accumulated in a relatively deep-water environment. Across the rest of the accumulation zone, by contrast, water levels appear to have been shallow. Sedimentation during this phase was dominated by autochthonous plant-organic-rich deposits, with minor fine-grained clastic input. Deposition was intermittently interrupted by localised episodes of mass movement that reworked the regolith mantling the steep internal slopes of the crater into the accumulation zone in the form of low-angle fans. At the broad scale, the sedimentology of Lake Lanotō displays similarities with that of volcanic calderas and maar lakes. However, the morphological simplicity of the basin, the general absence of contemporaneous volcanic activity, the timing of the onset of lacustrine conditions, the derivation of the clastic deposits in the volcanic crater almost solely from the by-products of the volcanic eruption, and the high biological activity in the lake waters mean that there are important differences between the types and distribution of sedimentary facies identified in Lake Lanotō and those represented in models of deposition in maars and volcanic calderas. 相似文献
14.
Geomorphic, lithologhic, and stratigraphic field studies as well as pollen data and mineralogical study have been used to
propose Pliocene and Pleistocene paleogeographic reconstructions of the El’gygytgyn meteorite crater area. The moment of impact
is recorded above the early Pliocene hill denudation plain as a “chaotic horizon” consisting of fragments of impactite rocks.
This chaotic horizon lies between layers of late Pliocene alluvial sediments. During the second half of the late Pliocene,
the region was tectonically active, when the Anadyr lowland was uplifted causing alluvial sediments to accumulate in the basins
to the south of the crater. Regional climatic cooling, which supported the spread of tundra and the formation of permafrost
is characteristically to late Pliocene. The 35–40 m high terrace that roughly follows the 530 m contour interval along the
Enmyvaam River formed during the middle Pleistocene. This terrace represents the maximum lake level. Erosion and incision
of the upper Enmyvaam River increased due to another wave of uplift. Additionally, El’gygytgyn Lake discharge increased causing
lake level to begin to drop in the Middle Pleistocene. Cooling continued, which led to the development of herb-dominated arctic
tundra. middle and late Pleistocene glaciations did not reach the El’gygytgyn lake region. The 9–11 m high lacustrine terrace
was formed around the lake during the late Pleistocene and the 2–3 m high lacustrine terrace formed later during the Holocene.
During the last 5000 years, the lake level has continued to drop as the modern coastline developed.
This is the third in a series of eleven papers published in this special issue dedicated to initial studies of El’gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
15.
A survey of the modern physical setting of Lake El’gygytgyn, northeastern Siberia, is presented here to facilitate interpretation
of a 250,000-year climate record derived from sediment cores from the lake bottom. The lake lies inside a meteorite impact
crater that is approximately 18 km in diameter, with a total watershed area of 293 km2, 110 km2 of which is lake surface. The only surface water entering the lake comes from the approximately 50 streams draining from
within the crater rim; a numbering system for these inlet streams is adopted to facilitate scientific discussion. We created
a digital elevation model for the watershed and used it to create hypsometries, channel networks, and drainage area statistics
for each of the inlet streams. Many of the streams enter shallow lagoons dammed by gravel berms at the lakeshore; these lagoons
may play a significant role in the thermal and biological dynamics of the lake due to their higher water temperatures (>6°C).
The lake itself is approximately 12 km wide and 175 m deep, with a volume of 14.1 km3. Water temperature within a column of water near the center of this oligotrophic, monomictic lake never exceeded 4°C over
a 2.5 year record, though the shallow shelves (<10 m) surrounding the lake can reach 5°C in summer. Though thermally stratified
in winter, the water appears completely mixed shortly after lake ice breakup in July. Mean annual air temperature measured
about 200 m from the lake was −10.3°C in 2002, and an unshielded rain gage there recorded 70 mm of rain in summer of 2002.
End of winter snow water equivalent on the lake was approximately 110 mm in May 2002. Analysis of NCEP reanalysis air temperatures
(1948–2002) reveals that the 8 warmest years and 10 warmest winters have occurred since 1989, with the number of days below
−30°C dropping from a pre-1989 mean of 35 to near 0 in recent years. The crater region is windy as well as cold, with hourly
wind speeds exceeding 13.4 m s−1 (30 mph) typically at least once each month and 17.8 m s−1 (40 mph) in winter months, with only a few calm days per month; wind may also play an important role in controlling the modern
shape of the lake. Numerous lines of evidence suggest that the physical hydrology and limnology of the lake has changed substantially
over the past 3.6 million years, and some of the implications of these changes on paleoclimate reconstructions are discussed.
This is the second in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
16.
Piero Guilizzoni Aldo Marchetto Andrea Lami Frank Oldfield Marina Manca Claudio A. Belis Anna M. Nocentini Patrizia Comoli Vivienne J. Jones Steve Juggins Christina Chondrogianni Daniel Ariztegui John J. Lowe David. B. Ryves Richard W. Battarbee Tim C. Rolph Julieta Massaferro 《Journal of Paleolimnology》2000,23(2):117-127
We report the results of analyses of pigments (derived from algae and photosynthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cladocerans, chironomids) in two late Pleistocene sediment cores from Lago Albano, a crater lake in Central Italy. The record contains evidence for oscillations in lake biota throughout the period ca. 28 to 17 k yr BP. The earliest of these are contained in the basal 3.5 m of light olive-gray and yellowish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. The later oscillations are best represented in the more extended sediment sequence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infer an initially low lake level rising to permit sediment accumulation at site 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remains are interbedded with laminated silts and carbonates. These sediments span the period ca. 24 to 17 k yr and are interpreted as representing, respectively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually independent chronological constraints on the frequency and duration of the oscillations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as responses to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duration suggest that at least some of these changes may parallel both the Dansgaard-Oeschger events recorded in Greenland Ice Cores and the contemporary oscillations in North Atlantic circulation documented in marine sediment cores. 相似文献
17.
The Holocene history of West Basin Lake,Victoria, Australia; chemical changes based on fossil biota and sediment mineralogy 总被引：4，自引：0，他引：4
Peter A. Gell Philip A. Barker Patrick De Deckker William M. Last Ljubica Jelicic 《Journal of Paleolimnology》1994,12(3):235-258
Analyses of diatoms, ostracods, pollen and sediment mineralogy from a 524 cm core from a stratified, hypersaline crater lake, West Basin, Victoria, has revealed clear shifts in the lake's water balance and chemistry and the region's climate over the last 10 000 years. Diatom and ostracod analyses reveal lake water salinity changes which are consistent with the conditions suitable for the precipitation of the carbonate and other minerals identified using x-ray diffraction analysis. The fluctuations in lake water balance deduced from diatom and ostracod inferred lake salinity suggest that the lake began to fill at the beginning of the Holocene and was saline and shallow. Toward the mid-Holocene the water levels rose and yet the lake remained largely saline. The late Holocene is marked by a return to more shallow but fluctuating, water conditions. Through the whole period, the regional dryland vegetation was dominated by open sclerophyll woodland. Both the lacustrine and regional environments interpreted here are consistent with those from Holocene records elsewhere in the region.This is the fourth in a series of papers published in this issue on the paleolimnology of arid regions. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. R. Chivas served as guest editor for these papers. 相似文献
18.
Diatom surface sediment samples and corresponding water chemistry were collected from 56 lakes across a natural conductivity gradient in western Uganda (reflecting a regional climatic gradient of effective moisture) to explore factors controlling diatom distribution. Here we develop a regional training set from these crater lakes to test the hypothesis that this approach, by providing more appropriate and closer analogues, can improve the accuracy of palaeo-conductivity reconstructions, and so environmental inferences in these lake systems compared to larger training sets. We compare this output to models based on larger, but geographically and limnologically diverse training sets, using the European Diatom Database Initiative (EDDI) database. The relationships between water chemistry and diatom distributions were explored using canonical correspondence analysis (CCA) and partial CCA. Variance partitioning indicated that conductivity accounted for a significant and independent portion of this variation. A transfer function was developed for conductivity (r jack 2 ?=?0.74). Prediction errors, estimated using jack-knifing, are low for the conductivity model (0.256 log10 units). The resulting model was applied to a sedimentary sequence from Lake Kasenda, western Uganda. Comparison of conductivity reconstructions using the Ugandan crater lake training set and the East Africa training set (EDDI) highlighted a number of differences in the optima of key diatom taxa, which lead to differences in reconstructed values and could lead to misinterpretation of the fossil record. This study highlights issues of how far transfer functions based on continental-scale lake datasets such as the EDDI pan-African models should be used and the benefits that may be obtained from regional training sets. 相似文献
19.
Laura S. Epp Kathleen R. Stoof Martin H. Trauth Ralph Tiedemann 《Journal of Paleolimnology》2010,43(4):939-954
Using molecular genetic methods and an ancient DNA approach, we studied population and species succession of rotifers of the
genus Brachionus in the Kenyan alkaline-saline crater lake Sonachi since the beginning of the 19th century as well as distribution of Brachionus haplotypes in recent and historic sediments of other lakes of the East African Rift System. The sediment core record of Lake
Sonachi displays haplotypes of a distinct evolutionary lineage in all increments. Populations were dominated by a single mitochondrial
haplotype for a period of 150 years, and two putatively intraspecific turnovers in dominance occurred. Both changes are concordant
with major environmental perturbations documented by a profound visible change in sediment composition of the core. The first
change was very abrupt and occurred after the deposition of volcanic ash at the beginning of the 19th century. The second
change coincides with a major lake level lowstand during the 1940s. It was preceded by a period of successively declining
lake level, in which two other haplotypes appeared in the lake. One of these putatively belongs to another species documented
in historical and recent Kenyan lake sediments. The analysis of plankton population dynamics through historical time can reveal
patterns of population persistence and turnover in relation to environmental changes. 相似文献
20.
A reconstruction of the hydrological and environmental evolution of the crater lake at Malha (Northern Darfur, Sudan) resulted from the mineralogical and biological study of a 9.21 m section of lake sediments, representing an uninterrupted sequence of lacustrine deposition since 8 290 14C years BP.Important changes in water supply and conditions of sedimentation are reflected in the nature of the sediments and the morphology and stratigraphical distribution of various salt minerals. Additional information on lake circulation patterns and salinity conditions are obtained from associated benthic paleocommunities, represented by ostracods and dipterid larvae. Combining both lines of evidence, the studied sequence can be divided in six distinct sections, which correspond to six successive periods in the lake's Holocene history. The first three periods, generally characterized by high lake levels, represent three generations of a meromictic lake, two of which have ended with a complete desiccation of the lake basin. Meromixis was stable during Period I, due to wind shelter and pronounced density stratification. In the course of Periods II and III stratification was repeatedly interrupted. During Period II, the disruptions were accompanied by important water budget fluctuations; a superimposed gradual decrease in net water supply eventually resulted in holomictic conditions terminating this period. Evidence of turbulence periodically affecting profundal waters is recorded in the sediments of Period III, suggesting that disruptions of stratification were now initiated by very strong winds. Between Period I and Period III, the littoral mixolimnion gradually evolved from near fresh to mesosaline. In Periods IV to VI, lake level was intermediate to low. The lake was holomictic for most of the time and meso- to hypersaline; during Period V, it repeatedly shrunk to a shallow brine pool.The Holocene evolution of Malha Crater Lake illustrates the progressive increase in aridity over most of North Africa following a well-established, early- to mid-Holocene major humid episode. The uninterrupted sedimentary sequence lends itself for detailed reconstruction of Holocene climatic evolution in arid Northeast Africa, a region where records of continuous lacustrine deposition are extremely scarce. As the chronology of critical events in the lake's history remains as yet unsupported by radiocarbon dates, correlation with other Holocene sequences in the eastern Sahara is highly tentative at this point. 相似文献